[Bug 1383334] Re: simple C++ program exhibits data corruption when compiled with -fstrict-aliasing

[Miklos Reiter]

I have re-submitted this bug report to the Linaro bug tracker:
https://bugs.linaro.org/show_bug.cgi?id=933


** Bug watch added: Linaro Bug Tracking System #933
   https://bugs.linaro.org/show_bug.cgi?id=933

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https://bugs.launchpad.net/bugs/1383334

Title:
  simple C++ program exhibits data corruption when compiled with
  -fstrict-aliasing

Status in “gcc-4.8-armhf-cross” package in Ubuntu:
  New

Bug description:
  When cross-compiled using the command line:
  $ arm-linux-gnueabihf-g++-4.8 -fPIC -o armGccBugTest armGccBugTest.cpp -std=c++11 -Wall -O2
  the attached program generates the incorrect output:
  # clobbered_pair: 0x00000000, 0x00000000
  # clobbered_pair: 0x88888888, 0x44444444

  The correct output is:
  # clobbered_pair: 0x00000000, 0x00000000
  # clobbered_pair: 0x00000000, 0x00000000
  This is produced as expected when compiling with:
  $ arm-linux-gnueabihf-g++-4.8 -fPIC -o armGccBugTest armGccBugTest.cpp -std=c++11 -Wall -O2 -fno-strict-aliasing
  (Also, compiling to the native x86-64 architecture using g++-4.8 produces correct output using either optimization settings.)

  The data from the ticks_t instance created on line 33 ends up
  overwriting the temporary pair_t() passed in the fourth argument to
  print_clobbered_pair(). Inspecting the disassembled code of the main
  function, it seems that the compiler attempts to re-use the temporary
  default-constructed pair_t() created on line 31 for the second call to
  print_clobbered_pair() on line 34. However, the memory location on the
  stack has been overwritten with the ticks_t instance created on line
  33.

  (We have reduced the problem to the attached minimal test case from a
  much more complicated system. Details such as the seemingly
  unnecessary user-defined copy constructor of the struct ticks_t or the
  unused arguments of the function print_clobbered_pair() are essential
  to reproducing the problem.)

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: g++-4.8-arm-linux-gnueabihf 4.8.2-16ubuntu4cross0.11
  ProcVersionSignature: Ubuntu 3.13.0-37.64-generic 3.13.11.7
  Uname: Linux 3.13.0-37-generic x86_64
  ApportVersion: 2.14.1-0ubuntu3.5
  Architecture: amd64
  CurrentDesktop: X-Cinnamon
  Date: Mon Oct 20 15:15:20 2014
  ProcEnviron:
   TERM=xterm
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_GB.UTF-8
   SHELL=/bin/bash
  SourcePackage: gcc-4.8-armhf-cross
  UpgradeStatus: No upgrade log present (probably fresh install)

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